Your uncle must be very close to you for him to ask you to be his executor. And it is really good that you are asking this question now, before you say yes.
Very simply said, an executor is responsible for carrying out the instructions in the will, whatever those may be. And you can still be an executor if you are also an heir. If you agree to be his executor, your uncle should give you a copy of his will and you should discuss with him anything that seems unclear. Once you have had that talk, there are a few things you should do right away.
First of all, if your uncle has not yet prepared his will, he should talk to an experienced attorney. It is very important that his will be legal and binding so that it will do the things he intends. If he has written his will without an attorney, you should encourage him to have it reviewed by an attorney and to be sure it was executed so that it is legal and binding.
Second, keep a copy of the will in your safety deposit box.
Third, encourage your uncle to review and revise his will at least every couple of years, and especially if his family or assets change.
Once all of that is done, you do not have any additional duties until your uncle’s death. When that occurs, though, there is a lot that must be done. The most important thing is to contact an experienced attorney right away to determine if a probate is needed for your uncle’s estate. Some assets may pass automatically to heirs, like property that might be held jointly with your aunt, but other property will require a probate of your uncle’s estate to transfer to the heirs. An experienced attorney will be able to let you know right away what is necessary to transfer your uncle’s property and will guide you through the probate process.